Insulated terminal



Nov. 15, 1955 R. L. SIMPKINS ET AL 2,724,092

INSULATED TERMINAL Filed May 8, 1951 IN VEN TOR. Poms/e7" L, Sfuwwws BY How/m0 A. (522/0 '1- United States Patent INSULATED TERMINAL Robert L. Simpkins, Royal Oak, John S. Materka, Dearborn, and Howard A. Elliott, Detroit, Mich, assignors to Essex Wire Corporation, Detroit, Mich a corpora tion of Michigan Application May 8, 1951, Serial No. 225,104 2 Claims. (Cl. 339-46) The present invention relates to an insulated terminal, and more particularly to an insulated terminal adapted for use with spark plugs and having pressure relief means provided therein to prevent the terminal from being blown off the electrode of the spark plug by internal pressure. The present construction is an improvement over our co-pending application Serial No. 208,768 on Insulated Terminal, filed January 31, 1951.

In insulated terminal constructions such as the one disclosed in the above-mentioned co-pending application, the terminal is well sealed and free from leaks so as to prevent moisture and dirt from affecting the efficiency of the spark plug. However, it has been found in certain instances that an internal pressure is built up at the electrode of the spark plug which results in blowing the terminal off the spark plug electrode. This internal pressure is due to the leakage of air or combustion gases at the electrode of the spark plug. One of the best known makes of spark plug produces a leakage of slightly below two cubic centimeters per minute, and other plugs which have been tested produce a leakage in excess of five cubic centimeters per minute. Some plugs have been found in all makes which even exceed the five cubic centimeter rate. Tests have proven that even two cubic centimeters leakage is sufficient to build up pressure in a well insulated terminal to cause it to balloon or blow off the spark plug after several minutes accumulation of the pulsations of cylinder pressure.

In dealing with this problem, it was discovered that it is impractical to attempt to alter the spark plug in order to decrease or prevent leakage. Therefore, the problem devolved into a necessity for a new and improved terminal.

Accordingly, it is a primary object of the present invention to provide an improved spark plug terminal which is effectively sealed against moisture and dirt and which includes means for releasing internal pressures built up therein by leakage of air at the spark plug electrode.

It is a further object of the present invention to provide such a terminal which is simple and easy to manufacture by mass production methods at low cost and wherein the pressure relief means is normally closed to keep out moisture and dirt, which pressure relief means will open only upon exertion of internal pressures.

Other objects of this invention will appear in the following description and appended claims, reference being had to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.

In the drawings:

Fig. 1 is a side elevation of an insulated terminal embodying the present invention,

Fig. 2 is an enlarged side elevation of the insulated terminal shown in Fig. 1 but with a portion broken away to illustrate the internal construction, and

Fig. 3 is an end elevation of the terminal shown in Figs. 1 and 2.

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Before explaining the present invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

A preferred embodiment of the present invention is disclosed in the drawing wherein a cable 10 comprises the wire 12 and the surrounding insulating material 14. The elbow terminal 16 includes the conductor-receiving leg 18 and the electrode-receiving leg 20. Proper electrical contact is maintained between the cable 10 and the conductor-receiving leg 18 by any suitable construction such as the inwardly extending nib 19 which pierces the insulation 14 and contacts the wire 12 of the cable 10. The elongated holes 22 in the electrode-receiving leg 20 are provided to give the electrode-receiving leg 20 more flexibility. A shield 24 is fitted over the electrode-receiving leg 20 to prevent molding material from entering the interior of the terminal 16 through the holes 22 when the protective cap 26 of insulating material is molded into place.

As explained in co-pending application Serial No. 208,768, the cap 26 is molded over the terminal 16 and cable 10 and the unit is cured, forming a homogeneous bond at X in the drawings. This construction prevents the usual leaks at this point which allow moisture and dirt to seep in onto the spark plug electrode.

The pressure relief means shown in the drawing is the pierced hole 28. It is important that the hole 28 be pierced rather than molded since a molded hole would be open at all times and would allow moisture and dirt to seep in onto the spark plug electrode. However, a pierced hole will normally be closed. It acts like a valve in that when the internal pressure exceeds the tensile strength of the part, the air is forced out through the hole. When the internal pressure is below the tensile strength of the part the hole remains closed and no moisture or dirt is permitted to enter.

It has been found that the location of the pressure relief means should be placed above the porcelain of the plug and may be anywhere up to the elbow of the terminal. In the drawing, Fig. 2, the hole 28 is shown extending through one of the holes 22 in the terminal 16.

Although other size holes can be used, the optimum hole range is from .031 to .062 inches. It has been found below .020 inch production difliculties arise because of the small size of the piercing needle and lack of mechanical strength. Holes larger than .187 inch are objectionable because they are so large that water can seep in with little effort.

From the above description it will be seen that we have provided an improved insulated terminal which embodies simple and efficient means for overcoming the prominent problem of terminal blow off.

Having thus described our invention, we claim:

1. An insulated terminal comprising a metal sleeve type shell having a conductor-receiving portion and an electrode-receiving portion, a conductor having insulating material thereon extending into said conductor-receiving portion and in direct contact therewith, an insulating cap disposed around said shell and the adjacent portion of r said insulated conductor and bonded to the insulating material on the conductor, normally closed pressure relief disposed in said cap adjacent the electrodereceiving portion, said pressure relief means being adapted to open and provide a passage between the interior of the terminal and the atmosphere to effect relief of excessive internal pressures and prevent failure or blowing ofi of the terminal when it is disposed on an electrode.

.2. An insulated sleeve-type elbow terminal particularly adapted for use with a spark plug comprising an inner elbow-shaped metal shell having a conductor-receiving leg and an electrode-receiving leg, said electrodereceiving leg having elongated holes therein to impart elasticity thereto, a conductor having insulating material thereon extending into said conductor-receiving leg and having a portion in direct contact with said conductorreceiving leg, and a cap of protective material disposed over said terminal and the adjacent portion of said conductor andbonded to the insulating material on said conductor, said cap extending beyond the free end of the electrode-receiving leg to provide a protective cover for a spark plug, and normally closed pressure relief means disposed in said cap adjacent the electrode-receiving leg, said pressure relief means being adapted to open and provide a passage between the interior of the terminal and the atmosphere to effect relief of excessive internal pressures and prevent failure or blowing off of the terminal when it is disposed on an electrode.

References Cited in the file of this patent UNITED STATES PATENTS LeGrand Apr. 24, 

